Bay Area Rapid Transit Director Joel Keller wants to pass a bill that would make it illegal for individuals to take up more than one seat on the train. Call it the one-seat-per-butt rule. Keller told the San Francisco Chronicle's Michael Cabanatuan that the measure is not intended to target homeless people; it's really aimed at everyone, including "people with backpacks, with luggage, with other things occupying seats." Fed up commuters are bound to approve.

BART is experiencing record ridership -- which makes BART riders cranky and envious of those who can sit and avoid the human crush. But whom does Keller think he's kidding when he says his proposal isn't aimed at the homeless? If a simply inconsiderate passenger is taking up an extra seat for a backpack or luggage, another commuter will ask that person to make room. It's only when the two-seat hog seems hostile, mentally ill or inebriated that others hesitate to inquire. Smell is also a factor.

During the winter months, the homeless can be especially vexing. When you are riding the train to work, it's irritating to see others taking up space during heavy commuting hours in an effort to stay warm and dry. The public pays fares to use BART as a conveyance, not to ride in railcars that double as homeless shelters (for which working stiffs also pay).

Also contributing to the dysfunction: Once you pay the minimum fare, you can ride all day; some charities give BART tickets to homeless people, ostensibly to help them travel for job interviews or social services. They mean well, but everyone would be better-served if their charitable dollars went to shelters period, not to turn BART into a shelter.

Keller is not your hardcore law-and-order type. He knows that riders usually resolve seat disputes; there shouldn't have to be a law to enforce the one-seat-per-butt concept. But without an ordinance, BART police have no leverage -- other than asking politely -- when someone wants to splay his or her bounty over multiple seats. Keller doesn't want BART police to enforce the policy when trains aren't full. He's open to reducing the proposed fine of $100 for a first offense or even issuing warnings only for first offenses.

Homeless riders are not the only offenders, Keller told me. He has heard tales of inconsiderate commuters who, when asked, refuse to move their backpacks, laptops or makeup kits to accommodate fare-paying fellow travelers. Boo, hiss on them.

Last month, I had a sit-down with BART Police Department Deputy Chief Benson Fairow, as I've wondered about what can be done to ease the commute for people who rely on BART to get to work or school. BART has heard from many like-minded riders who don't understand why police cannot do more. "Put yourself in the police officer's shoes," Fairow told me. "I don't get to pick who I serve." The police cannot treat someone on BART differently for looking as if he or she does not have a good reason to be there.

He's right. Point taken. That's why Keller's modest idea makes sense. It is directed at all seat hogs, unless they have a physiological reason for occupying two seats.

Next job: Clean up downtown San Francisco BART stations.

When you get off BART at the Civic Center and Powell Street stations, you see people sleeping in de facto encampments in hallways -- and the platforms stink of urine. In bad weather, walking through Civic Center and Powell stations can feel downright menacing. When taxpayers don't feel safe taking BART, when all they see is squalor, they will find other ways to get around -- and that defeats the whole idea.